Application or injection of chemicals, such as fertilizers, on or into the soil, is commonly used to enhance growth and yield for agricultural plants. In come cases, such substances are in fluid-form (liquid or gaseous phase, as opposed to solid phase). Apparatus is required to convey the substance from a bulk storage container to the ground.
One example is the injection of anhydrous ammonia (NH3) (a gas at ambient temperatures and pressures) into the ground. Normally, the substance is kept under pressure in liquid phase in a large bulk holding container or tank. What are called knives have discharge ends that are dragged through the ground. A valving and distribution system can be selectively operated to convey anhydrous ammonia from the tank to the knives as the knives are dragged through the ground to emplace the fertilizer in the ground. Nitrogen fertilizer is a major input in terms of cost and energy in production of major crops (e.g. corn, wheat, cotton, rice). Anhydrous ammonia is the most popular form of nitrogen fertilizer application.
Physical properties of anhydrous ammonia can cause it to convert from a high pressure liquid to a mixture of liquid and gas as it travels through application equipment. The mixture is very difficult to evenly distribute to individual application knives across the swath width of the applicator. These distribution problems may be the cause of over-application. Because liquid ammonia is much more dense than gaseous form, openings that receive greater proportions of liquid ammonia will distribute more nitrogen to their knives than openings that receive greater proportions of gaseous ammonia. This results in often highly variable application across the applicator swath.
Normally some type of manifold is used to distribute anhydrous ammonia from the tank to a plurality of knives, so that in one pass, a plurality of rows can be fertilized. During the past 10 years, new low pressure anhydrous ammonia manifolds have been developed. Each manifold has some potential to improve upon the widely varying distribution of the 40-year-old “conventional” radial outlet manifold.
The present inventors conducted studies of several types of commercially available distribution manifolds. Eight manifolds were evaluated during field application at application rates of 84 kg N/ha (75 lb N/ac) and 168 kg N/ha (150 lb N/ac). The actual ammonia stream from each outlet of the manifold was collected and weighed after each run to determine mean, % difference from mean, highest outlet to lowest outlet weight ratio, and the coefficient of variation (“CV”) for each run with 11 knife outlets. Results showed that the use of the older “conventional” manifold can result in coefficient of variation or CV values in excess of 30%. Some studies indicate as much as a four-to-one shank-to-shank output variation across an applicator. In general, all the newer manifold designs tested reduced this value, some achieving CV values in the 5% range. But some still have on the order of two-to-one variation between shanks. During application the operator cannot tell if there is over- or under-application. The term CV or coefficient of variation, as used herein, is in percentage as a statistical indicator of variation in output of each manifold. The lower, the better. The coefficient of variation is a well-known indicator. (See, e.g., Steel, R. G., J. H. Torrie, and D. A. Dickey. Principles and Procedures of Statistics: A Biometrical Approach. 3 ed. McGraw-Hill Companies, Inc. New York. 1997 Pg. 26-27; and ASAE (American Society of Agricultural Engineers) S386.2 DEC98 Calibration and Distribution Pattern Testing of Agricultural Aerial Application Equipment, ASAE—The Society for engineering and agricultural, food, and biological systems, 2950 Niles Rd., St. Joseph, Mich. 49085-9659; and ASAE (American Society of Agricultural Engineers) S341.3 FEB99 Procedure for Measuring Distribution Uniformity and Calibrating Granular Broadcast Spreaders, ASAE—The Society for engineering and agricultural, food, and biological systems, 2950 Niles Rd., St. Joseph, Mich. 49085-9659).
The above-mentioned testing of existing distribution manifolds show there is room for improvement in distribution from the holding container to the application knives. Even a reduction of a few percent of anhydrous ammonia use by improved application equipment and methods could materially decrease the amount of nitrogen release (including into surface and ground water resources) as well as cost to the producers. Some of the existing distribution systems tested (on a three-point DMI model 3250 anhydrous ammonia applicator) include:
Rotaflow™ from H. I. Fraser Pty LTD (Sydney, Australia)—top feed rotary with flow of material though impeller, not outside it.
Equaflow™ from PGI Intl.—Rotary outlets with internal cavity size manually controlled by user.
Vertical Dam designs (small and large, cotton or corn rings) from Continental NH3 Products—ammonia enters from side and swirls into radial outlets.
Conventional manifolds (Model 3497) from Continental NH3 Products (one with mixer; one with nipple; one with street elbow). Also, a COLD-FLO® System 16 (#20340 canister and separate 16 outlet distribution manifolds.) Also, side entry linear and tee entry linear manifold designs and a FD-1200 (CDS John Blue Co.) were tested.
There is a need for optimization of distribution. Development of such a manifold is vital to the future use of this fertilizer form in precision agriculture applications including variable rate application and late spring side dressing of ammonia. Existing manifold designs exhibit noticeable variation as they distribute anhydrous ammonia fertilizer to each of the injection knives on the toolbar applicator. This can lead in the field to nitrogen deficiencies, adversely affecting yield or excesses, adversely affecting environmental quality.
Four measures of variability among outlet distribution were computed. Average outlet difference is the average absolute difference in kg(lb)NH3 of all outlets from the mean output of all outlets for a particular test plot. The average percentage outlet difference is the average of absolute outlet difference from the mean outlet output expresses a percentage of a mean outlet output. This percentage measures use to indicate the average percentage each outlet is from the mean application rate and to normalize variability based on the ammonia collected during each plot run. High/low ratio is the ratio of the ammonia weight from the outlet with the greatest output to the outlet with the least output for a specific application. Coefficient of variation (CV) among the outlets was also included.
Variability among entry methods for the conventional manifolds was different for the lower application rate but at the higher rate, all conventional manifolds had equal variability. The COLD-FLO® manifold had greater variability than all other manifolds tested. The lowest variability across the outlets was measured with the Rotaflow™ and small-housing vertical-dam manifolds at both application rates. Although the small-housing vertical-dam had low variability, it also had a lower flow rate through the manifold and subsequent lower application rate for the same regulator setting. A general trend of decreasing variability with increasing manifold pressure was seen.
Further discussion of problems with present distribution manifolds is set forth at “Rate Variability of Anhydrous Ammonia Applicator Equipment”, ISU Extension publication PM-1747, and “Improving the Uniformity of Anhydrous Ammonia Application”, Iowa State University, University Extension publication PM 1875 (June 2001), both incorporated by reference herein.
Vertical dam manifolds and the COLD-FLO® system try to solve the gas/liquid mixture problem by separating gas and liquid phases and metering equal portions of each to each knife.